The modern communications era has brought about a tremendous proliferation of wireline and wireless networks. Computer networks, television networks, and telephony networks in particular are experiencing an unprecedented technological expansion, fueled by consumer demand. The ever-increasing need for bandwidth has exceeded even the most perspicacious expectations, as the explosion of data and multimedia transmissions are breaking the seams of the networking infrastructure. This has propelled an intense effort to quickly increase the available communications bandwidth.
In line with this effort, various data transmission technologies have been employed and improved upon. Improved networking architectures and protocols over copper wires, radio waves and fiber-optic cable are helping in the effort to increase available bandwidth. Of late, optical data communication over the fiber-optic infrastructure is proving to be one of the most promising areas to assist in this effort. The fiber-optic cabling laid over the last couple of decades have traditionally been underused with respect to bandwidth. Essentially, this has been due to the failure to multiplex signals on a given fiber. For example, the first major use of optical fiber was a single-mode use where a single signal is transmitted through the fiber. In this mode, service providers quickly experience fiber exhaustion such that bandwidth can no longer be increased unless more fibers are installed.
Efforts have turned to modulation techniques used to transmit the optical signals. In order to increase bandwidth, wavelength division multiplexing (WDM) has been used to allow multiple signals to travel along a single fiber. Wavelength division multiplexing (WDM) is a technique where multiple signals having different wavelengths are launched on the same fiber and demultiplexed at the receiving end. Each optical signal is assigned to a frequency (wavelength) within a designated frequency band, and the individual signals are multiplexed onto a single fiber where they can be collectively amplified. The first such use was to allow two different signals at two different wavelengths to travel along a fiber, which essentially doubled the bandwidth available for each fiber. The original two-wavelength mode communicated optical signals at about 1300 nm and 1550 nm. This additional bandwidth, while beneficial, was very quickly devoured by the unforeseeably immense demand for bandwidth. It became apparent that further increases in bandwidth capacity would be necessary, and the focus turned to increasing the number of wavelength-modulated signals transmitted through the fiber. This effort has had some success using WDM technology, and is generally referred to as dense WDM (DWDM). Initially, WDM was employed in SONET (Synchronous Optical NETwork) or SDH (Synchronous Digital Hierarchy) systems, and is currently being implemented in true optical networks that utilize optical cross-connects and amplifiers to transmit optical signals over long distances without the need for electrical regeneration.
As the bandwidth of these optical links and networks increases, so does the need for restoring optical links in the event of a cable break or other impairment to fiber-optic communication. This network resilience is often accomplished by reserving a portion of the fibers in a particular configuration for restoration in the event of a working channel failure. The type of optical protection scheme employed may depend on the type of network architecture implemented. Linear structures, including one or more point-to-point WDM connections, as well as WDM ring and mesh structures are common types of network structures associated with WDM transmission technology.
In linear or point-to-point systems, the associated protection scheme monitors for a fault on the line, such as the loss of a signal. When this occurs, signals transmitted on the working line are switched so that they travel along a backup or “protection” line. For linear architectures, this can be done in a variety of ways, including 1+1 or 1:1 protection schemes. A 1+1 protection typically refers to an automatic protection switch based on pairing one working link with one backup link. The signal is transmitted in parallel on both links so that if the working link fails, the receiver node switches the connection from working to backup. A 1:1 protection refers to an automatic protection switch that is also based on a working link with a backup link, but the protected signals are not transmitted on both links in parallel. It is possible to send lower priority signals on the backup link. Where the working link fails, the protected signals will be switched from the working link to the backup link, and the lower priority signals on the backup link (if any) will be preempted. Protection for point-to-point connections is often referred to as “sub-network connection protection” (SNCP) because it is performed at the channel or link level, and not at the network level.
While these types of protection are generally used for linear topologies, they may also be used in other topologies such as ring and mesh topologies. When the optical channel (OCH) 1+1 protection is used in a ring topology, it is similar to the SONET UPSR protection scheme. 1+1 and 1:1 protection schemes require 100% spare bandwidth to backup the working link. Therefore, a shared protection scheme for ring or mesh topologies includes backup links that are shared by several working links. One example of the ring protection is optical multiplexer section shared protection ring (OMS-SPRING) that is similar to the SONET MS-SPRING. This is accomplished by reversing the line or switching multiplexed signals from the working line to a backup line. The signals will then travel around the ring and enter the target node from the opposite side.
However, in networks exhibiting other than a strict linear or ring topology, a signal may be faced with a variety of alternate protection routes if the working path fails. For example, “mesh” network topologies can become quite convoluted and may be comprised of various segments of ring and linear topologies. Even the simplest mesh network topology can be viewed as a ring topology with a central node connected to multiple nodes of the ring. For example, referring to FIG. 1, an example of a simple mesh network is illustrated. The network 10 includes nodes A 12, B 14, C 16 and D 18 respectively. Nodes A, B, C and D form a ring, and node E is a central node connected to each of the other nodes. This configuration forms a “mesh” network topology.
In the case of a ring topology, protection fibers form a ring analogous to the working ring. A signal transmitted along such protection fibers essentially has one physical route in which the signal can take, which is around the ring. In the case of a mesh topology, it can be seen from FIG. 1 that there are many different possible routes between any two given nodes. For example, if the working fiber from node A 12 to node B 14 to node D 18 were to fail between nodes A 12 and B 14, it must be determined what path the signal will take between node A 12 and node D 18 once transferred to the protection fiber. The signal could be transmitted along protection fiber from node A 12 to node E 20 to node D 18. Alternatively, the signal could be transmitted from node A to E to C to D, or A, C, D, and so forth. It can be seen that there are multiple routes between any given nodes in the network. As can be seen, an increase in the number of nodes and corresponding links in the mesh configuration causes an increasing number of potential routes between nodes.
The restoration of optical communication via protection paths in a mesh topology therefore requires consideration of the physical network topology. Further, the speed and efficiency in switching from working fibers to protection fibers must be considered to maintain high quality network resilience. In prior art mesh networks, protection paths consist of predetermined alternate paths, or real-time calculated alternate paths, which are set up after the source node recognizes that a link has failed. This requires that the source node first be notified of the link failure, and then requires the nodes along the alternate path to later be switched to allow the information from the failed link to be re-routed along the alternate path. The prior art requires the source node to send the switching request over the signaling or supervisory channel to the nodes along the alternate path. The source node may request the acknowledgement information from the nodes relating to the switch status or availability. This time-consuming and inefficient process adversely affects recovery time.
It would be desirable to have a system and method for providing efficient and flexibility of routing within the network of protection fibers where there are multiple available routes in which the optical signal may travel. The present invention provides a solution to the aforementioned and other shortcomings of the prior art, and offers additional advantages over existing prior art technologies.